Ultra‐High Proton/Vanadium Selectivity for Hydrophobic Polymer Membranes with Intrinsic Nanopores for Redox Flow Battery

Abstract

with Nafi on/SiO 2 hybrid membrane at the current density, 10 mA cm −2 . [ 10 ] Apart from the modifi cation of Nafi on membrane, the enhanced performances of VRB were recently also achieved with several kinds of sulfonated aromatic polymers in terms of the minimized hydrophilic domains. [11][12][13] Therefore, it is understood that the control of hydrophobic nature seems to be a common way to reduce the vanadium cross-over.More recently, Zhang et al. reported a VRB with a nanofi ltration type porous membrane that achieved competitive performances, a CE up to 95% and an EE of 76%. [ 14 ] The working principle has been based on the size sieving separation owing to the quite different size of proton and vanadium ions. [ 15 ] This strategy offers not only tremendously decreased cost owing to the already commercialized product, but also an ultimate insight toward maximizing H + /V selectivity. If the pore size of the membrane only enables protons (or water) transfer, the maximized performances could be achieved through the maximized H + /V selectivity. Thus, the subnano-sieving membrane for proton permselective transport is challenging. Here we report a fundamentally new concept to realize such proton/ vanadium selectivity. The concept is unprecedented as the material is hydrophobic, does not swell in water, contains micro porosity hosting water molecules along which protons can migrate and does not allow any other (vanadium) whatsoever. The proposed working principle of such hydrophobic polymers with intrinsic microporosity is disclosed in Scheme 1 .PIM-1 is the fi rst generation polymer having an intrinsic microporosity. We hypothesize that these materials can transport protons preferentially in VRBs because of its hydrophobic molecular structure, limited swelling in aqueous solution, inherent microporous structure with a pore diameter less than 2 nm, high free volume fraction above 20%, good solution processability, and relatively slow physical ageing compared to other high free volume polymers. [16][17][18] Even though hydrophobic, its microporosity is suspected to transport water molecules at high rates: Kentish and co-workers demonstrated water vapor permeation through PIM-1 at no fewer than 30 000 Barrer (1 Barrer = 10 −10 cm 3 (STP) cm (cm 2 s cm Hg) −1 ) above a water activity of 0.7. [ 19 ] Yet, little is known about the state of water inside such microporous polymers: one may anticipate the water being preferentially partitioned in the free-volume forming the microporosity rather than being absorbed into the polymer matrix. This could imply that a certain degree of proton transfer could occur by water molecules inside PIM-1. Meanwhile, the partitioning of hydro-solvated vanadium ions is expected to be limited by both the small radius of its pores and the difference of dielectric property, as illustrated in Scheme 1 .Recent increasing interest in the integration of renewable energy sources has accelerated efforts to develop electric energy storage (EES). [ 1,2 ] Among many approaches for EES, the allvanad...

Potential of sodium alginate/titanium oxide biomembrane nanocomposite in DMFC application

“…Figure 1 shows the surface with low magnification, cross section, and surface with high-magnification FESEM images of five membranes: Figures 1A to 1C with optimum loading has resulting membrane the compress structures (nonporous) and a homogeneous morphology. The morphology of the SA membrane differs from other porous structure membranes, likes PBI and PIM-1 membranes, 42,43 but it resembles a SPEEK membrane. 36 The solid membrane structure is a good feature for proton conductivity and reduces the rate of loss of methanol fuel.…”

“…The crystalline structure of TiO 2 changed the membrane morphology. The morphology of the SA membrane differs from other porous structure membranes, likes PBI and PIM-1 membranes, 42,43 but it resembles a SPEEK membrane. 44 The homogeneous TiO 2 distribution increases the ion selectivity for the SA biomembrane.…”

Polymers of Intrinsic Microporosity in Triphasic Electrochemistry: Perspectives

“…These have been shown to provide proton permeability whilst stopping vanadium cross-over. [33] In poly-sulfide redox flow systems PIMs have been shown to inhibit poly-sulfide crossover. [34,35,36,37,38] Selective permeability to small ionic species was shown in many cases to provide excellent separator performance based on PIMs.…”

A Bunch-Like Tertiary Amine Grafted Polysulfone Membrane for VRFBs with Simultaneously High Proton Conductivity and Low Vanadium Ion Permeability

“…To address this challenge, several kinds of novel concept membranes have recently been fabricated for potential application in VRFBs. These membranes are based on the conducting proton and V‐blocking synergy design, such as the amphoteric ion exchange membrane and porous membranes . Although these membranes achieved superior ionic selectivity, the lower proton conductivity compared to PEMs and AEMs, and the heterogeneous pore size is still a challenge for large‐scale application in VRFBs …”